Magnetic tunnel junction (MTJ) free layer damping reduction

ABSTRACT

In one embodiment, a system includes a sensor, the sensor having a free layer, a ferromagnetic spin sink layer spaced from the free layer, the spin sink layer being operative to reduce a spin-induced damping in the free layer during operation of the sensor, and a nonmagnetic spacer layer positioned between the free layer and the spin sink layer, the spacer layer having a long spin-diffusion length.

CROSS REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/884,480, filed on Jan. 31, 2018, which is a continuation applicationof U.S. patent application Ser. No. 15/673,816, filed on Aug. 10, 2017(now U.S. Pat. No. 9,911,439), which in turn is a continuationapplication of U.S. patent application Ser. No. 15/195,947, filed onJun. 28, 2016 (now U.S. Pat. No. 9,734,850), the entireties of which areincorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to data storage systems, and moreparticularly, this invention relates to reducing Gilbert damping of thefree layer in the magnetic tunnel junction of magnetic heads andmagnetic random access memory devices.

BACKGROUND

The heart of a computer is a magnetic hard disk drive (HDD) whichtypically includes a rotating magnetic disk, a slider that has read andwrite heads, a suspension arm above the rotating disk and an actuatorarm that swings the suspension arm to place the read and/or write headsover selected data tracks on the rotating disk. The suspension armbiases the slider into contact with the surface of the disk when thedisk is not rotating but, when the disk rotates, air is swirled by therotating disk adjacent an air bearing surface (ABS) of the slidercausing the slider to ride on an air bearing a slight distance from thesurface of the rotating disk. When the slider rides on the air bearingthe write and read heads are employed for writing magnetic impressionsto and reading magnetic signal fields from the rotating disk. The readand write heads are connected to processing circuitry that operatesaccording to a computer program to implement the writing and readingfunctions.

The volume of information processing in the information age isincreasing rapidly. In particular, it is desired that HDDs be able tostore more information in their limited area and volume. A technicalapproach to meet this desire is to increase the capacity by increasingthe recording density of the HDD. To achieve higher recording density,further miniaturization of recording bits is effective, which in turntypically requires the design of smaller and smaller components.

With advances in higher recording density, however, secondary factorssuch as damping caused by magnetism of the free layer have becomeimportant. As areal density increases, magnetic noise caused by thedamping coefficient of the free layer becomes a limiting factor toincrease the signal-to-noise ratio (SNR). It would be desirable,therefore, to develop a system that lowers the damping coefficient,thereby lowering the noise and allowing the highest possible SNR.

SUMMARY

In one embodiment, a system includes a sensor, the sensor having a freelayer, a ferromagnetic spin sink layer spaced from the free layer, thespin sink layer being operative to reduce a spin-induced damping in thefree layer during operation of the sensor, and a nonmagnetic spacerlayer positioned between the free layer and the spin sink layer, thespacer layer having a long spin-diffusion length.

Any of these embodiments may be implemented in a magnetic data storagesystem such as a disk drive system, which may include a magnetic head, adrive mechanism for passing a magnetic medium (e.g., hard disk) over themagnetic head, and a controller electrically coupled to the magnetichead.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings.

FIG. 1 is a simplified drawing of a magnetic recording disk drivesystem, according to one embodiment.

FIG. 2A is a cross-sectional view of a perpendicular magnetic head withhelical coils, according to one embodiment.

FIG. 2B is a cross-sectional view a piggyback magnetic head with helicalcoils, according to one embodiment.

FIG. 3A is a cross-sectional view of a perpendicular magnetic head withlooped coils, according to one embodiment.

FIG. 3B is a cross-sectional view of a piggyback magnetic head withlooped coils, according to one embodiment.

FIG. 4 is a schematic representation of a perpendicular recordingmedium, according to one embodiment.

FIG. 5A is a schematic representation of a recording head and theperpendicular recording medium of FIG. 4, according to one embodiment.

FIG. 5B is a schematic representation of a recording apparatusconfigured to record separately on both sides of a perpendicularrecording medium, according to one embodiment.

FIG. 6 is a schematic representation of portions of the magnetic tunneljunction according to one embodiment.

FIG. 7 is a graph showing the damping coefficients for variousembodiments.

FIG. 8A is a graph showing ferromagnetic resonance (FMR) of the effectof an iron spin sink layer according to one embodiment.

FIG. 8B is a graph of the magnetization of including an iron spin sinklayer according to one embodiment using a vibrating sample magnetometer(VSM).

FIG. 9 is a schematic representation of a portion of the magnetic tunneljunction according to one embodiment.

FIG. 10A is a schematic representation of portions of the magnetictunnel junction according to one embodiment.

FIG. 10B is a schematic representation of portions of the magnetictunnel junction according to one embodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

The following description discloses several preferred embodiments ofmagnetic storage systems and/or related systems and methods, as well asoperation and/or component parts thereof.

In one general embodiment, a system includes a sensor, the sensor havinga free layer, a ferromagnetic spin sink layer spaced from the freelayer, the spin sink layer being operative to reduce a spin-induceddamping in the free layer during operation of the magnetic head, and anonmagnetic spacer layer positioned between the free layer and the spinsink layer, the spacer layer having a long spin-diffusion length.

Referring now to FIG. 1, there is shown a disk drive 100 in accordancewith one embodiment of the present invention. As shown in FIG. 1, atleast one rotatable magnetic medium (e.g., magnetic disk) 112 issupported on a spindle 114 and rotated by a drive mechanism, which mayinclude a disk drive motor 118. The magnetic recording on each disk istypically in the form of an annular pattern of concentric data tracks(not shown) on the disk 112. Thus, the disk drive motor 118 preferablypasses the magnetic disk 112 over the magnetic read/write portions 121,described immediately below.

At least one slider 113 is positioned near the disk 112, each slider 113supporting one or more magnetic read/write portions 121, e.g., of amagnetic head according to any of the approaches described and/orsuggested herein. As the disk rotates, slider 113 is moved radially inand out over disk surface 122 so that portions 121 may access differenttracks of the disk where desired data are recorded and/or to be written.Each slider 113 is attached to an actuator arm 119 by means of asuspension 115. The suspension 115 provides a slight spring force whichbiases slider 113 against the disk surface 122. Each actuator arm 119 isattached to an actuator 127. The actuator 127 as shown in FIG. 1 may bea voice coil motor (VCM). The VCM comprises a coil movable within afixed magnetic field, the direction and speed of the coil movementsbeing controlled by the motor current signals supplied by controller129.

During operation of the disk storage system, the rotation of disk 112generates an air bearing between slider 113 and disk surface 122 whichexerts an upward force or lift on the slider. The air bearing thuscounter-balances the slight spring force of suspension 115 and supportsslider 113 off and slightly above the disk surface by a small,substantially constant spacing during normal operation. Note that insome embodiments, the slider 113 may slide along the disk surface 122.In other embodiments the bearing may comprise a gas other than air, e.g.helium.

The various components of the disk storage system are controlled inoperation by control signals generated by controller 129, such as accesscontrol signals and internal clock signals. Typically, control unit 129comprises logic control circuits, storage (e.g., memory), and amicroprocessor. In a preferred approach, the control unit 129 iselectrically coupled (e.g., via wire, cable, line, etc.) to the one ormore magnetic read/write portions 121, for controlling operationthereof. The control unit 129 generates control signals to controlvarious system operations such as drive motor control signals on line123 and head position and seek control signals on line 128. The controlsignals on line 128 provide the desired current profiles to optimallymove and position slider 113 to the desired data track on disk 112. Readand write signals are communicated to and from read/write portions 121by way of recording channel 125.

The above description of a magnetic disk storage system, and theaccompanying illustration of FIG. 1 is for representation purposes only.It should be apparent that disk storage systems may contain a largenumber of disks and actuators, and each actuator may support a number ofsliders.

An interface may also be provided for communication between the diskdrive and a host (integral or external) to send and receive the data andfor controlling the operation of the disk drive and communicating thestatus of the disk drive to the host, all as will be understood by thoseof skill in the art.

Regarding a magnetic head, an inductive write portion therein includes acoil layer embedded in one or more insulation layers (insulation stack),the insulation stack being located between first and second pole piecelayers. A gap may be formed between the first and second pole piecelayers by a gap layer at an air bearing surface (ABS) of the writeportion. The pole piece layers may be connected at a back gap. Currentsare conducted through the coil layer, which produce magnetic fields inthe pole pieces. The magnetic fields fringe across the gap at the ABSfor the purpose of writing bits of magnetic field information in trackson moving media, such as in tracks on a rotating magnetic disk.

The second pole piece layer has a pole tip portion which extends fromthe ABS to a flare point and a yoke portion which extends from the flarepoint to the back gap. The flare point is where the second pole piecebegins to widen (flare) to form the yoke. The placement of the flarepoint directly affects the magnitude of the magnetic field produced towrite information on the recording medium.

FIG. 2A is a cross-sectional view of a perpendicular magnetic head 200,according to one embodiment. In FIG. 2A, helical coils 210 and 212 areused to create magnetic flux in the stitch pole 208, which then deliversthat flux to the main pole 206. Coils 210 indicate coils extending outfrom the page, while coils 212 indicate coils extending into the page.Stitch pole 208 may be recessed from the ABS 218. Insulation 216surrounds the coils and may provide support for some of the elements.The direction of the media travel, as indicated by the arrow to theright of the structure, moves the media past the lower return pole 214first, then past the stitch pole 208, main pole 206, trailing shield 204which may be connected to the wrap around shield (not shown), andfinally past the upper return pole 202. Each of these components mayhave a portion in contact with the ABS 218. The ABS 218 is indicatedacross the right side of the structure.

Perpendicular writing is achieved by forcing flux through the stitchpole 208 into the main pole 206 and then to the surface of the diskpositioned towards the ABS 218.

FIG. 2B illustrates one embodiment of a piggyback magnetic head 201having similar features to the head 200 of FIG. 2A. As shown in FIG. 2B,two shields 204, 214 flank the stitch pole 208 and main pole 206. Alsosensor shields 222, 224 are shown. The sensor 226 is typicallypositioned between the sensor shields 222, 224.

FIG. 3A is a schematic diagram of another embodiment of a perpendicularmagnetic head 300, which uses looped coils 310 to provide flux to thestitch pole 308, a configuration that is sometimes referred to as apancake configuration. The stitch pole 308 provides the flux to the mainpole 306. With this arrangement, the lower return pole may be optional.Insulation 316 surrounds the coils 310, and may provide support for thestitch pole 308 and main pole 306. The stitch pole may be recessed fromthe ABS 318. The direction of the media travel, as indicated by thearrow to the right of the structure, moves the media past the stitchpole 308, main pole 306, trailing shield 304 which may be connected tothe wrap around shield (not shown), and finally past the upper returnpole 302 (all of which may or may not have a portion in contact with theABS 318). The ABS 318 is indicated across the right side of thestructure. The trailing shield 304 may be in contact with the main pole306 in some embodiments.

FIG. 3B illustrates another embodiment of a piggyback magnetic head 301having similar features to the head 300 of FIG. 3A. As shown in FIG. 3B,the piggyback magnetic head 301 also includes a looped coil 310, whichwraps around to form a pancake coil. Sensor shields 322, 324 areadditionally shown. The sensor 326 is typically positioned between thesensor shields 322, 324.

In FIGS. 2B and 3B, an optional heater is shown near the non-ABS side ofthe magnetic head. A heater (Heater) may also be included in themagnetic heads shown in FIGS. 2A and 3A. The position of this heater mayvary based on design parameters such as where the protrusion is desired,coefficients of thermal expansion of the surrounding layers, etc.

FIG. 4 provides a schematic diagram of a simplified perpendicularrecording medium 400, which may also be used with magnetic diskrecording systems, such as that shown in FIG. 1. As shown in FIG. 4, theperpendicular recording medium 400, which may be a recording disk invarious approaches, comprises at least a supporting substrate 402 of asuitable non-magnetic material (e.g., glass, aluminum, etc.), and a softmagnetic underlayer 404 of a material having a high magneticpermeability positioned above the substrate 402. The perpendicularrecording medium 400 also includes a magnetic recording layer 406positioned above the soft magnetic underlayer 404, where the magneticrecording layer 406 preferably has a high coercivity relative to thesoft magnetic underlayer 404. There may one or more additional layers(not shown), such as an “exchange-break” layer or “interlayer”, betweenthe soft magnetic underlayer 404 and the magnetic recording layer 406.

The orientation of magnetic impulses in the magnetic recording layer 406is substantially perpendicular to the surface of the recording layer.The magnetization of the soft magnetic underlayer 404 is oriented in (orparallel to) the plane of the soft underlayer 404. As particularly shownin FIG. 4, the in-plane magnetization of the soft magnetic underlayer404 may be represented by an arrow extending into the paper.

FIG. 5A illustrates the operative relationship between a perpendicularhead 508 and the perpendicular recording medium 400 of FIG. 4. As shownin FIG. 5A, the magnetic flux 510, which extends between the main pole512 and return pole 514 of the perpendicular head 508, loops into andout of the magnetic recording layer 406 and soft magnetic underlayer404. The soft magnetic underlayer 404 helps focus the magnetic flux 510from the perpendicular head 508 into the magnetic recording layer 406 ina direction generally perpendicular to the surface of the magneticmedium. Accordingly, the intense magnetic field generated between theperpendicular head 508 and the soft magnetic underlayer 404, enablesinformation to be recorded in the magnetic recording layer 406. Themagnetic flux is further channeled by the soft magnetic underlayer 404back to the return pole 514 of the head 508.

As noted above, the magnetization of the soft magnetic underlayer 404 isoriented in (parallel to) the plane of the soft magnetic underlayer 404,and may represented by an arrow extending into the paper. However, asshown in FIG. 5A, this in plane magnetization of the soft magneticunderlayer 404 may rotate in regions that are exposed to the magneticflux 510.

FIG. 5B illustrates one embodiment of the structure shown in FIG. 5A,where soft magnetic underlayers 404 and magnetic recording layers 406are positioned on opposite sides of the substrate 402, along withsuitable recording heads 508 positioned adjacent the outer surface ofthe magnetic recording layers 406, thereby allowing recording on eachside of the medium.

Except as otherwise described herein with reference to the variousinventive embodiments, the various components of the structures of FIGS.1-5B, and of other embodiments disclosed herein, may be of conventionalmaterial(s), design, and/or fabricated using conventional techniques, aswould become apparent to one skilled in the art upon reading the presentdisclosure.

Gilbert damping is a force that opposes the precessions of the magneticspins created from the free layer in a magnetic device. The damping canbe translated into thermal magnetic noise, using the Gilbert dampingcoefficient, which has been shown to be inversely proportional tosignal-to-noise ratio (SNR) such that increased reader magnetic noise,e.g., lowers SNR. In magnetic heads, it would be advantageous to lowerthe thermal magnetic noise generated by damping from the free layer.

In a magnetic random access memory (MRAM) device, lowering the effect ofdamping is critical for lowering the switching current as applied to lowpower memory applications. Contemplated approaches employ a magnesiumoxide (MgO) cap to suppress spin pumping to lower the dampingcoefficient. Specifically, the MgO cap reflects the spin currentgenerated by the free layer back into the free layer. However, thetypically thick MgO cap used in this case may not be practical for lowresistant area (RA) products, for example, MTJs in magnetic heads. Themagnetic heads have a lower resistance tolerance than MRAM. Reducing thedepth of the MgO cap decreases the resistance; but if the cap is toothin, then there is less effect on reducing the dampening effect and theRA is detrimentally affected. Damping can also be modified by varyingthe materials that form the free layer; however, such an approach mayalso unfavorably change other properties of the free layer.

Various embodiments described and/or suggested herein overcome theforegoing challenges by inserting a spacer with long spin diffusionlength between the free layer and a ferromagnetic (FM) layer, which canmodify the damping without modifying the constituents of the free layer.

FIG. 6 depicts a system 600 having an element 601 in accordance with oneembodiment. As an option, the present system 600 may be implemented inconjunction with features from any other embodiment listed herein, suchas those described with reference to the other FIGS. Of course, however,such system 600 and others presented herein may be used in variousapplications and/or in permutations which may or may not be specificallydescribed in the illustrative embodiments listed herein. Further, thesystem 600 presented herein may be used in any desired environment.

The system 600 may be a magnetic recording device such as a magneticdata storage drive. The element 601 may be a magnetic sensor of suchmagnetic recording device. In other embodiments, the system 600 may bean MRAM device. The element 601 may be a component of a memory cell,e.g., a magnetic tunnel junction (MTJ), of such MRAM device.

Referring now to FIG. 6, in some embodiments, the element 601 of system600 includes a free layer 602, and a ferromagnetic spin sink layer 604spaced from the free layer 602, the spin sink layer 604 being operativeto reduce a spin-induced damping in the free layer 602 during operation.For example, upon passage of a current therethrough by read channelcircuitry of a controller in one embodiment.

The element 601 further includes a nonmagnetic spacer layer 603positioned between the free layer 602 and the spin sink layer 604, and acap layer 606. Positioned on an opposite side of the free layer 602 area tunnel barrier layer 608 and a reference layer 610. The free layer602, tunnel barrier layer 608, reference layer 610 and cap layer 606 maybe of conventional construction.

The spacer layer 603 may have a long spin-diffusion length, for example,when constructed of copper, such that electrons can travel across thespacer layer 603 without scattering or flipping. The polarization of theelectrons tends to be undisturbed by such a layer with a long spindiffusion length. However, a layer of material with a short spindiffusion length, such as tantalum in the cap layer 606 would create anenvironment for spin scatter resulting in a damping effect and spinpumping.

Insertion of a spin sink layer 604 on an opposite side of the spacerlayer 603 as the free layer 602, modifies the damping generated by thefree layer, where such damping is dependent on the composition of thespin sink layer 604. FIG. 7 illustrates the ferromagnetic resonance(FMR) measurement of the Gilbert damping coefficient α (y axis of FIG.7) of sample element compositions according to some approaches. Thedamping coefficient α for the free layer is 0.014 (dotted line, FIG. 7).For comparison, the graph shows two different compositions of the spinsink layer (604 in FIG. 6) each with a copper spacer layer (603 in FIG.6) positioned between the cap layer (606 in FIG. 6, in this caseRu—Ta—Ru, and depicted as Ru in FIG. 7) and the free layer (602 in FIG.6). Placing the copper spacer between the cap layer containing rutheniumRu and the free layer shows that the damping coefficient of the freelayer is unchanged with the damping coefficient at the expected 0.014(dotted line, FIG. 7). In contrast, insertion of a spin sink layerbetween the copper layer and the cap layer has a remarkable effect onthe damping coefficient α. Nickel (Ni in FIG. 7) is a material known tohave a very high damping effect, and as such the presence of Ni in thespin sink layer seems to increase the damping coefficient of the freelayer (from 0.014 to nearly 0.015, FIG. 7). Iron (Fe in FIG. 7) is amaterial known to have a low damping effect, and as such the presence ofFe in the spin sink layer seems to significantly decrease the dampingcoefficient of the free layer (from 0.014 to less than 0.0125, FIG. 7).Thus, in some embodiments, the damping generated by the free layer maybe modified with a spin sink layer via the spacer without modifying thefree layer.

In one embodiment, the spacer layer 603 may be comprised of copper whichhas a very long spin diffusion length, greater than 100 nm. Moreover, aspacer layer 603 of copper of only 4 nm may be essentially transparentto the electrons traveling through the layer. In other embodiments, thespacer layer 603 may be any nonmagnetic conductive metals with a longspin diffusion length, for example, silver-tin alloys, silver and gold,and alloys of silver and gold.

In some approaches, the deposition thickness of the spacer layer 603 maybe below a spin diffusion length, as determined by conventional methods,of a material composition of the spacer layer 603. For example, althoughthe spin diffusion length of copper is 100 nm and so a Cu spacer layerwith any thickness well below the spin diffusion length may be used, theoptimal thickness for the spacer layer within the element may be about 4nm, e.g., to fit within a structure having a defined shield-to-shieldread gap.

Furthermore, in yet another embodiment, the deposition thickness of thespacer layer 603 may be sufficient to prevent substantial magneticcoupling of the free layer 602 and the spin sink layer 604. In optimalconditions, the deposition thickness of the spacer layer 603 may allowthe free layer 602 to synchronize with the spin sink layer 604independent of magnetic coupling, and thus the damping effect may bereduced. In sharp contrast, less desirable approaches demonstrate thatabsence of the spacer layer may cause the spin sink layer to becomemagnetically coupled to the free layer thereby becomingindistinguishable from the free layer and changing the total moment ofthe free layer, which is an important parameter to control in a magneticrecording head.

As further illustrated in FIGS. 8A-8B, in preferred embodiments, theposition of the spacer layer sandwiched between the free layer and thespin sink layer may allow the spin sink layer and free layer to functionin coupled oscillation (FIG. 8A) while being magnetically decoupled fromeach other (FIG. 8B). A graph of the derivative of FMR (FIG. 8A) showsthe spin sink layer (Fe) functions independent of the free layer (Free)when a spin reflective layer (MgO) is inserted between the spin sinklayer and the copper spacer/free layer (see solid line, FIG. 8A). Thespin sink layer oscillates at a different frequency than the free layeras indicated by the second peak in the sample with the spin reflectivelayer (solid line). In contrast, without the MgO layer, the free layer(Free) and the spin sink layer (Fe), with the copper (Cu) layer inbetween, are synchronized as shown by the single peak and the absence ofthe second peak (circle line, FIG. 8A). The peak for the coupledoscillation shows similar behavior to the FMR response of the free layerby itself without an additional spin sink layer (square line, FIG. 8A).The inventors believe that the coupled oscillation of the spin sinklayer on top of the free layer with the spacer layer in betweencontributes to the spin sink layer regulation of the damping of the freelayer, while this effect is removed by insertion of an MgO layer thatreflects the spin current.

In a preferred embodiment, the presence of the spacer layer between thefree layer and the spin sink layer allows the two layers to bemagnetically decoupled as demonstrated in FIG. 8B which depicts themagnetization of sensor samples using a vibrating sample magnetometer(VSM). The presence of the copper spacer (Cu) between the free layer(Free) and the spin sink layer (Fe) (circle line, FIG. 8B) shows twodistinct magnetic hysteresis loops compared to the single loop shownwith copper spacer alone and no additional ferromagnetic spin sink layer(square line, FIG. 8B). As expected and similar to the configuration ofFree-Cu—Fe sensor (circle line, FIG. 8B), the presence of the spinreflective layer, MgO (solid line, FIG. 8B) above the spin sink layershow similar magnetization properties by VSM. The inventors believe bothsensor samples, with the Cu-spin sink layer configuration either with orwithout MgO demonstrate that the spin sink layer is magneticallydecoupled from the free layer.

With continued reference to FIG. 6, in some embodiments the spin sinklayer 604, or ferromagnetic layer, may have a deposition thickness in arange of about 1 nm to about 5 nm, preferably about 2 nm. In someapproaches, the spin sink layer 604 may be composed of ferromagneticmaterial, for example, iron, nickel, cobalt, Heusler alloys such asCo₂MnGe, and combinations thereof.

FIG. 9 depicts a system 900 having an element 901 in accordance with oneembodiment. As an option, the present system 900 may be implemented inconjunction with features from any other embodiment listed herein, suchas those described with reference to the other FIGS. Of course, however,such system 900 and others presented herein may be used in variousapplications and/or in permutations which may or may not be specificallydescribed in the illustrative embodiments listed herein. Further, thesystem 900 presented herein may be used in any desired environment.

The system 900 may be a magnetic recording device such as a magneticdata storage drive. The element 901 may be a magnetic sensor of suchmagnetic recording device. In other embodiments, the system 900 may bean MRAM device. The element 901 may be a component of a memory cell,e.g., a magnetic tunnel junction (MTJ), of such MRAM device.

As depicted in the system 900 in FIG. 9, a preferred embodiment of theelement 901 includes a spin reflective layer 905 that may be added tofurther modify the damping effect of the free layer 902. The spinreflective layer 905 is preferably positioned below the cap layer 906,on an opposite side of the spin sink layer 904 than the spacer 903 andfree layer 902. In some embodiments, the spin reflection layer 905 maybe comprised of a material having spin reflective properties, such asmagnesium oxide, tantalum oxide, ruthenium oxide, hafnium oxide, etc, orby oxidizing the top surface of the ferromagnetic spin sink layer 904.In some approaches, the deposition thickness of the spin reflectionlayer may be within a range of about 0.1 to about 1 nm. In a preferredembodiment, the thickness of the spin reflection layer will be optimallythin enough for optimal resistance and thick enough for optimalreflection.

FIG. 10A-B depicts systems 1000, 1009 having a sensor in accordance withadditional embodiments. As an option, the present systems 1000, 1009 maybe implemented in conjunction with features from any other embodimentlisted herein, such as those described with reference to the other FIGS.Of course, however, such systems 1000, 1009 and others presented hereinmay be used in various applications and/or in permutations which may ormay not be specifically described in the illustrative embodiments listedherein. Further, the systems 1000, 1009 presented herein may be used inany desired environment.

The systems 1000, 1009 may be magnetic recording devices such as amagnetic data storage drive. In other embodiments, the systems 1000,1009 may be MRAM devices.

As depicted in the system 1000 in FIG. 10A, a preferred embodiment ofthe element 1001 illustrates a floating shield design that may include anonmagnetic cap layer 1006 above the spin sink layer 1004. In someapproaches, the top shield 1007 may be positioned above the nonmagneticcap layer 1006 and the spin sink layer 1004 may be positioned betweenthe spacer layer 1003 and the cap layer 1006. The spacer layer 1003 inthe floating shield design (depicted in FIG. 10A) allows the spin sinklayer 1004 to float, or be magnetically decoupled, from the free layer1002, while the cap layer 1006 allows the spin sink layer 1004 to bemagnetically decoupled from the top shield 1007. While the precisemechanism is not known, and without wishing to be bound by any theory,the inventors believe the floating shield design improves linearresolution of the read head.

In system 1009 of FIG. 10B, the element 1008 may have a configuration asshown in FIG. 10B in which the spin sink layer 1004, using conventionalmethods, is stitched and magnetically coupled into the shield 1007;specifically, the top shield 1007 is positioned directly on the spinsink layer 1004. In some embodiments, the spin sink layer 1004 may betuned to the top shield 1007 so that the two layers may be properlyrecessed in the sensor 1008 configuration.

It should be noted that methodology presented herein for at least someof the various embodiments may be implemented, in whole or in part, incomputer hardware, software, by hand, using specialty equipment, etc.and combinations thereof.

Moreover, any of the structures and/or steps may be implemented usingknown materials and/or techniques, as would become apparent to oneskilled in the art upon reading the present specification.

The inventive concepts disclosed herein have been presented by way ofexample to illustrate the myriad features thereof in a plurality ofillustrative scenarios, embodiments, and/or implementations. It shouldbe appreciated that the concepts generally disclosed are to beconsidered as modular, and may be implemented in any combination,permutation, or synthesis thereof. In addition, any modification,alteration, or equivalent of the presently disclosed features,functions, and concepts that would be appreciated by a person havingordinary skill in the art upon reading the instant descriptions shouldalso be considered within the scope of this disclosure.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of an embodiment of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. A magnetic sensor comprising: a spin sink layerto reduce damping in a free layer of the magnetic sensor; a spacer layerbetween the free layer and the spin sink layer; and a spin reflectivelayer separated from the spacer layer by the spin sink layer.
 2. Themagnetic sensor of claim 1, further comprising a cap layer separatedfrom the spin sink layer by the spin reflective layer.
 3. The magneticsensor of claim 1, wherein the spin reflective layer comprises ones ofmagnesium oxide, tantalum oxide, ruthenium oxide, and hafnium oxide. 4.The magnetic sensor of claim 1, wherein the spin reflective layercomprises an oxidized portion of the spin sink layer.
 5. The magneticsensor of claim 1, wherein a deposition thickness of the spin reflectivelayer is at least one tenth of a nanometer and not more than onenanometer.
 6. The magnetic sensor of claim 1, wherein the spacer layeris nonmagnetic and comprises a spin diffusion length that is greaterthan a deposition thickness of the spacer layer.
 7. The magnetic sensorof claim 6, wherein the spin diffusion length of the spacer layer isabout one hundred nanometers and the deposition thickness of the spacerlayer is about four nanometers.
 8. The magnetic sensor of claim 1,wherein the spacer layer magnetically decouples the spin sink layer fromthe free layer.
 9. The magnetic sensor of claim 1, wherein the spacerlayer comprises at least one of copper, silver, tin, and gold.
 10. Themagnetic sensor of claim 1, wherein the spacer layer comprises anonmagnetic conductive metal having a spin diffusion length that permitselectrons to travel across the spacer layer without scattering orflipping.
 11. The magnetic sensor of claim 1, wherein the magneticsensor is part of a hard disk drive.
 12. The magnetic sensor of claim 1,wherein the magnetic sensor is part of a magnetic random access memorydevice.
 13. The magnetic sensor of claim 1, wherein the spin sink layercomprises a ferromagnetic material.
 14. The magnetic sensor of claim 1,wherein the spin sink layer reduces damping in the free layer via thespacer layer without modification of the free layer.
 15. The magneticsensor of claim 1, wherein the spin sink layer has a depositionthickness of at least one nanometer.
 16. A magnetic sensor comprising: aspin sink layer to reduce damping in a free layer of the magneticsensor; a nonmagnetic spacer layer between the spin sink layer and thefree layer; a cap layer separated from the nonmagnetic spacer layer bythe spin sink layer; and a top shield separated from the spin sink layerby the cap layer.
 17. The magnetic sensor of claim 16, wherein thenonmagnetic spacer layer magnetically decouples the spin sink layer fromthe free layer, and wherein the cap layer magnetically decouples thespin sink layer from the top shield.
 18. The magnetic sensor of claim16, wherein the nonmagnetic spacer layer comprises a spin diffusionlength that is greater than a deposition thickness of the nonmagneticspacer layer.
 19. A magnetic recording device comprising: a magneticsensor comprising: a free layer; a spin sink layer; a nonmagnetic spacerlayer between the spin sink layer and the free layer; and a spinreflective layer separated from the spacer layer by the spin sink layer.20. The magnetic recording device of claim 19, wherein the magneticrecording device is at least one of a magnetic random access memory anda hard disk drive.